Treatment of brain disease can be limited because of the difficulty of getting water-soluble drugs into the brain. The blood-brain barrier (BBB) restricts brain drug uptake due to its anatomical structure. Site-directed brain delivery is an ideal approach to overcome these limitations. At the BBB, there are proteins that transport water soluble nutrients such as glucose and amino acids into brain to enable normal function. Choline is an essential nutrient and is taken up into brain by a transport system as well. This transporter offers an opportunity as a vector-mediated system to deliver drugs to the brain. Our hypothesis is that the blood-brain barrier choline transporter will facilitate brain uptake of drugs that normally would not have access the brain. To be able to use this strategy to improve brain drug uptake, a full understanding of the active site substrate specificity of this transport protein is necessary. To investigate our hypothesis, we will use a combination of physiological and computer modeling based methods. The in situ brain perfusion method will be used in adult rats to evaluate BBB transport processes. We have shown that N-n-octyl nicotinium iodide (NONI) binds and is transported by this transporter. Further, NONI significantly blocks nicotine's effects in brain dopamine systems in vitro. We will further evaluate its brain uptake profile and the substrate specificity of the BBB transporter. Inhibitor constants (Ki) will be determined and compared to the Km of choline and Vmax values will be assessed to evaluate potential brain uptake. Molecular modeling maps and comparative molecular field analysis force fields will extend in vivo studies and reduce future need for animal studies. In vivo microdialysis will be used to evaluate changes in dopamine concentrations as a result of peripheral NONI administration. This application is a focused plan that will lead to development of new choline and nicotine analog drugs that will bind the BBB choline transporter and afford advances in therapy for brain disorders such as Parkinson's disease, Alzheimer's disease and stroke.